Knife holders for slitter winding machines and the like

ABSTRACT

A pressure fluid operated knife holder comprising a cylinder having a piston and piston rod therein, and a knife head carried by the piston rod. The piston, piston rod and knife head assembly are fluid pressure actuated from an upper limit position to a lower limit position in which a male knife on the head is positioned relative to a female knife. Adjustable means is provided for initially setting the cutting edge of the male knife relative to the female knife in the lower limit position of the assembly. The male knife is supported by a mounting axially movable in the knife head between inner and outer positions to set the male knife in cutting position against the female knife, and the mounting also has limited rocking movement to equalize contact pressure between the male and female knives. Outward axial displacement of the mounting to set the male knife is accomplished by pressure fluid from the cylinder and the connections from the cylinder to the knife head are constructed and arranged so that pressure fluid cannot flow from the cylinder to the knife head until the assembly is in the lower limit position. Pressure fluid admitted to the knife head is vented to atmosphere in all positions of the assembly except said lower limit position.

" United States Patent 91 J ohnstone 1 July 1,1975

[ KNIFE HOLDERS FOR SLITTER WINDING MACHINES AND THE LIKE [75] Inventor:Bruce V. Johnstone, Gap, Pa.

[73] Assignee: Johnstone Engineering & Machine Company, Parkesburg, Pa.

221 Filed: Feb.ll, 1974 211 App1.No.:441,207

[52] U.S. Cl. 83/469; 83/482; 83/501; 83/5081, 83/562 [51] Int. Cl. B23D19/00; 826D H14 [58] Field of Search 83/482,501, 502, 503, 83/562,508.2, 469

[56] References Cited UNITED STATES PATENTS 3,186,281 6/l965 Wingen83/501 X 3,380,330 4/1968 Gilmore 83/503 X Primary Examiner-Willie G.Abercrombie Attorney, Agent, or FirmHowson and Howson [57] ABSTRACT Apressure fluid operated knife holder comprising a cylinder having apiston and piston rod therein; and a knife head carried by the pistonrod. The piston, piston rod and knife head assembly are fluid pressureactuated from an upper limit position to a lower limit position in whicha male knife on the head is positioned relative to a female knife.Adjustable means is provided for initially setting the cutting edge ofthe male knife relative to the female knife in the lower limit positionof the assembly. The male knife is supported by a mounting axiallymovable in the knife head between inner and outer positions to set themale knife in cutting position against the female knife. and themounting also has limited rocking movement to equalize contact pressurebetween the male and female knives. Outward axial displacement of themounting to set the male knife is accomplished by pressure fluid fromthe cylinder and the connections from the cylinder to the knife head areconstructed and arranged so that pressure fluid cannot flow from thecylinder to the knife head until the assembly is in the lower limitposition. Pressure fluid admitted to the knife head is vented toatmosphere in all positions of the assembly except said lower limitposition.

21 Claims, 8 Drawing Figures KNIFE HOLDERS FOR SLI'I'TER WINDINGMACHINES AND THE LIKE This invention relates to new and usefulimprovements in knife holders for slitter winding machines and the like.More particularly, the invention relates to knife holders of the fluidpressure actuated type having separate means for lowering the kniferelative to the material to be cut and for laterally setting the kniferelative to the cooperating mating knife of the machine.

Prior knife holders of the type described are characterized by certainobjectionable features and disadvantages. For example, in some priorknife holders it frequently occurs that the lateral set or shift of themale knife relative to the female knife of the machine will commence ortake place before the male knife has reached the full lowered positionthereof in proper overlapping relation to the female knife of themachine thereby causing premature engagement of the knives withresulting damage to the male knife. Also, the construction andarrangement of some prior holders is such that when cutting heavy weightdense board with taped lapped splices sufficient resistance may bepresented to elevate the male knife when it is laterally set or shiftedand the male knife will engage and ride on the surface of the femaleknife as in a score type cut with resulting damage to the male blade.

Another objection to prior knife holders of the aforesaid type is thatthe construction and arrangement for mounting the male knife membercauses variations in the contact pressure between the male and femaleblades resulting in excessive wear of the blades. Also, in a number ofprior devices it is difficult to remove and replace the male knife onthe knife holder.

With the foregoing in mind, an object of the present invention is toprovide a novel knife holder of the type described that is constructedand arranged to prevent lateral setting or shifting of the male knifeuntil the latter has attained its fully lowered position in properoverlapping relation to the female knife of the machine.

Another object of the invention is to provide a knife holder of novelconstruction in which any tendency for the male knife to override thefemale knife of the machine is prevented.

Another object of the present invention is to provide a knife holderhaving the features and advantages set forth wherein the contactpressure between the male and female knives is substantially constant atall times.

A further object of the invention is to provide a novel knife holderconstruction in which removal and replacement of the male knife may bereadily and easily accomplished.

These and other objects of the invention and the various features anddetails of the construction and operation thereof and hereinafter fullyset forth and described with relation to the accompanying drawings, inwhich:

FIG. I is a side elevational view partially in section of a knife holderembodying the present invention showing the male knife actuating pistonin the raised inoperative position;

FIG. 2 is a front clevational view of the knife holder shown in FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view on line 33, FIG. 2;

FIG. 4 is a fragmentary sectional view of the upper portion of FIG. 3showing the male knife actuating piston and associated parts in thefully lowered operative position of the male knife;

FIG. 5 is a fragmentary sectional view on line 5-5, FIG. 3;

FIG. 6 is an enlarged partial sectional view on line 6-6, FIG. 1;

FIG. 7 is a view similar to FIG. 6 showing the male knife and itssupporting head in the fully lowered cutting position; and

FIG. 8 is a sectional view in reduced scale on line 8-8, FIG. 6.

Referring now to the drawings, FIGS. 1-3 thereof, show one embodiment ofthe present invention comprising a vertically disposed cylinder 1 havingan integral bracket portion 2 projecting laterally therefrom constructedand arranged for slidable mounting on the arbor 3 of a typical slitterwinding machine. The bracket 2 is fixedly secured to the arbor 3 bymeans of a Reid screw 4. The arbor 3 extends horizontally crosswise ofthe slitter winder machine, and customarily a plurality of knife holdersis mounted on the arbor 3 at spaced intervals therealong according tothe widths of the strips into which the web material is to be cut. Theindividual knife holders may be adjustably positioned and secured asdesired along the arbor 3 by loosening the Reid screw 4, grasping thehandle 5 and then retightening the Reid screw 4.

Referring more particularly to FIG. 3, the cylinder 1 has upper andlower annular end members 6 and 7, respectively, fixedly secured inplace by means of snap rings 8 and 9. The upper annular end member 6 isprovided with an annular packing ring 10 seated in an annular groove 11formed in the outer surface of the member 6 and disposed in sealingengagement with the adjacent inner wall surface of the cylinder I.Lining the interior wall of the cylinder 1 between the cylinder endmembers 6 and 7 is a tubular cylindrical sleeve 12 in which is slidablymounted an annular piston 13 of comparatively short axial length. Thepiston 13 is provided with piston ring 14 seated in a groove 15 and thering 14 has sliding sealing engagement with the inner wall surface ofthe cylinder sleeve 12.

The annular piston 13 is mounted on a piston rod 16 that extendscoaxially within the cylinder 1 and lining sleeve 12. The piston rod 16comprises an intermediate portion 17 that extends through the annularpiston 13 and has an external diameter substantially the same as theinternal diameter of the piston. A lower portion 18 of the piston rod 16has a larger diameter than the piston portion 17 and provides an annularshoulder 19 on which the piston 13 is seated and firmly secured on thepiston rod 16 by a snap ring 20. An O-ring type seal 21 is mounted inthe portion 17 of the rod 16 adjacent the annular shoulder 19.

The piston rod 16 also comprises an upper portion 23 having a diameterless than the intermediate portion I7 and a terminal end portion 24 ofless diameter than said portion 23. The rod portion 23 is externallythreaded as shown and threaded thereon is the internally threadedannular skirt portion 25 of an adjustment thimble 26 that also has arecess 25a of smaller diameter to receive the terminal end portion 24 ofthe piston rod 16. The purpose and operation of the adjustment thimble26 is hereinafter set forth. The adjustment thimble 26 extends coaxiallythrough the annular cylinder end member 6 and is rotatably adjustableaxially on the piston rod 16. A fluid pressure tight seal is providedbetween the adjustment thimble 26 and the cylinder end member 6 by apacking ring 27 recessed in the inner wall surface of said member 6. anda further seal between the end member 6 and thimble 26 is provided by anO-ring 28 seated in a recess 29 in the upper end face of the member 6and circumscribing the external surface of the adjustment thimble 26.

An expansion spring 30 is coiled about the lower portion 18 of thepiston rod l6 and acts between the lower cylinder end member 7 and thepiston 13 normally to urge said piston 13 and piston rod 16 upwardly tothe elevated or inoperative position of the knife holder shown in FIGS.1-3 of the drawings. In the illustrated embodiment of the invention thepiston 13 and piston rod 16 are actuated downwardly within the sleeve 12of cylinder l against the expansion force of the spring 30 by means ofair under pressure admitted to the cyl inder 1 above the piston 13through a suitable fitting 31.

As will be apparent from FIGS. 3 and 4 of the drawings. axial movementof the piston rod 16 in either di rection is accompanied by acorresponding axial move ment of the adjustment thimble 26 relative tothe annular cylinder end member 6. The upper limit position of thepiston assembly. comprising piston 13. piston rod 16 and adjustmentthimble 26, is fixedly determined by a snap ring 32 that is seated in agroove 33 formed in the outer surface of the skirt portion 25 of thethimble 26 and engages against the undersurface of the annular cylinderend member 6 as shown in FIG. 3. The adjustment thimble 26 is providedwith an enlarged head portion 34 and the lower limit position of thepiston assembly is fixedly determined by engagement of the undersurface35 of the thimble head portion 34 with the adja cent surface of thecylinder end member 6 as shown in FIG. 4 of the drawings. By thisconstruction and arrangement the stroke of the piston. rod and thimbleassembly is constant and equal to the axial distance between the snapring 32 and the undersurface 35 of the thimble head portion 34.

Referring to FIGS. 3, 6 and 7 of the drawings. the portion 18 of thepiston rod 16 extends slidably through the annular member 7 at the lowerend of the cylinder 1 and terminates at short distance therebelow. Thepiston rod 16 normally is secured against rotation relative to theannular end member 7 by means of a key 36 mounted in confronting keyways37 and 38 provided, respectively. in the piston rod portion 18 and endmem ber 7, for example. as shown in FIG. 5 of the drawings. The keymember 36 is secured in place by suitable fastening means such as ascrew 39 and the annular end member 7 is fixedly secured rotationallywith respect to the cylinder 1 by means of a set screw 40.

Secured to the lower end of the piston rod portion 18, for example bywelding 41, is a supporting head 42 for the male knife of the knifeholder. The head 42 is of cylindrical construction having an axialrecess 43 of relatively large diameter defined by a cylindrical internalwall surface 44 and an axial recess 45 of smaller diameter defined bythe cylindrical internal wall surface 46. The larger recess 43 ispartially closed by an annular end ring 47 secured in place. forexample. by screws 48 and the recess 45 is closed by an end plate 49secured in place. for example by screws 50.

Mounted axially in the head 42 for limited axial and rocking movementtherein is a bearing support. generally designated 51. comprising anannular member 52 disposed in the recess 43 and a member 53, secured tothe member 52 by screws 54, that projects axially within the recess 45and has an external diameter somewhat less than the diameter of the wall46 of said recess 45.

The peripheral surface 55 of the bearing support member 52 engages withthe circumscribing cylindrical wall surface 44 of the recess 43 and isprovided with an arcuate spherical surface contour as shown in FIGS. 6and 7 having a radius described from the center 0 located on the axis ofthe knife head 42.

The member 52 of the bearing support 51 includes an axially extendingannular sleeve portion 56 that projects endwise through the centralopening in the end ring 47 of the head 42, and the stub shaft 57 of aknife mounting plate 58 is rotationally mounted in said sleeve 56. forexample. by means of a bearing assembly 59. A male cutting knife 60 isfrictionally secured with respect to the plate 58, for example. by meansof a beveled snap ring 62 engaged in a suitable slot 63 in the mountingplate 58. The bearing assembly is secured in the sleeve 56, for example.by means of a snap ring 64 engaged in an internal groove 65 of saidsleeve.

Sufficient clearance is provided between the support member 52 and theend ring 47 of the head 42 to permit limited axial movement of thesupport 51 within the head 42 and. of course. any such axial movement ofthe support 52 is accompanied by a corresponding axial movement of themounting plate 58 and knife 60 carried thereby. Also. limited rockingmovement of the bearing support 51 about the center c within the head 42is afforded by the arcuate spherical peripheral surface 55 on the member52.

When the male knife 60 is inoperative. the mounting 51 normally ismaintained in the axial inward limit position thereof shown in FIG. 6.by means of a plurality of expansion coil springs 66 arranged in equallyspaced circumferential relation (see FIG. 8) and mounted in counterboredrecesses 67 in the member 52. The springs 66 react between the innersurface of the end ring 47 and annular shoulders 68 at the inner ends ofthe recesses 67. and smaller diameter passage 69 extend from each recess67 entirely through the member 52 to vent any pressure build-up betweenthe member 52 and head 42 that might tend to oppose actuation of themounting 51 to the inward limit position by the springs 66.

Actuation of the mounting 51 and knife 60 axially outward relative tothe head 42 to the operative position shown in FIG. 7 of the drawings isaccomplished by fluid pressure. such as air. admitted to the head recess45 and acting upon a flexible diaphragm 70 constructed and arranged asshown more particularly in FIGS. 6 and 7 of the drawings. The centralcircular portion 71 of the diaphragm 70 is adhesively secured to theadjacent surface of the bearing support member 53 and the peripheraledge portion 72 of said diaphragm 70 is fixedly secured in an annulargroove or recess 73 provided as shown in the head member 42. Thediaphragm 70 also includes an annular bellows type reversely foldedportion 73 surrounding the member 53 and interposed between the latterand the adjacent circumscribing wall surface 46 of the head member 42.

Pressure fluid is supplied to the recess 45 of the head 42 through aradial passage 74 formed in the closure plate 49 and terminating at itsouter end in an axial port 75 disposed in confronting communication withan axial passage 76 formed in the head member 42 and communicating atits inner end with a radial passage 77. At its outer end the passage 77in the head member 42 is in open communication with a coaxial recess 78provided in the lower end of the portion 18 of the piston rod 16, andcommunicating with said recess 78 is a passage 79 that extends coaxiallywithin the piston rod 16 for the entire length thereof as shown in FIG.3 of the drawings, the upper end of the passage 79 at the tip of theterminal end portion 24 of the piston rod 16 is in open communicationwith the recess 25a of the adjustment thimble 26.

As previously stated, a particular feature of the present invention isthe provision of a knife holder construction of the type described inwhich lateral setting of the knife is positively prevented and cannotoccur until the knife has been actuated to its fully lowered position inproper overlapping relation with the cooperating female knife of themachine. According to the invention this is accomplished by constructingand arranging the inlet port for the flow of pressure fluid from thecylinder 1 to the diaphragm chamber 45 so that said port is opened toreceive pressure fluid from the cylinder I only when the piston 13, rod16 and knife head 42 have been actuated to the lower limit position.Provision is also made to vent the diaphragm chamber 45 to atmosphere atall times except in the lower limit position of the piston assembly.

In the illustrated embodiment of the invention, a radial port 80 toreceive pressure fluid from the cylinder 1 is provided in the externalwall of the adjustment thimble 26 and is spaced vertically below theundersurface 35 of the thimble head 34 a predetermined distance slightlygreater than the thickness of the cylinder end member 6. By thisconstruction and arrangement it will be apparent that the port 80 isopen to the interior of the cylinder 1 to receive pressure fluid only inthe lower limit position of the piston, rod and thimble assemblydetermined by the under surface 35 of the thimble head 34, as shown inFIG. 4 of the drawings.

The radial port 80 at the inner end thereof communicates with a verticalpassage 81 in the wall of the thimble 26 and this passage 8]communicates at its upper end with a radial passage 82. The radialpassage 82 extends entirely through the thimble wall immediately belowthe head 34 of the thimble 26 and provides a vent for pressure fluidfrom the thimble chamber 25:: to the ambient atmosphere except in thelower limit position of the thimble in which the outer end of the ventpassage 82 is closed by the seal 28 in the cylinder end member 6 asshown in FIG. 4.

By virtue of the construction and arrangement shown and described,pressure fluid admitted to the cylinder 1 through fitting 31 cannotenter the port 80 and flow through the connecting passages and ports tothe diaphragm actuating chamber 45 in the head 42 until after thepressure fluid in the cylinder has actuated the piston rod and thimbleassembly to the lower limit position thereof shown in FIG. 4 of thedrawings. In the upper limit position of said assembly shown in FIG. 3,and in all intermediate positions thereof. the port 80 is closed tocommunication with the cylinder 1 and the vent passage 82 is open to theambient atmosphere.

Thus, at the end of a slitting operation during which the piston knifehead assembly is in the lower limit position upon cut-off of thepressure fluid supply to the cylinder 1, the spring 30 in the cylinder Iwill actuate the piston-knife-head assembly to the upper limit positionshown in FIG. 3. At the start of upward movement of thepiston-knife-head assembly the vent port 82 will be opened to atmosphereand pressure fluid in the diaphragm actuating system will immediately bevented to the atmosphere so that the springs 66 immediately return theknife 60 and mounting 51 axially to the inner limit position thereof asshown in FIG. 6.

In operation of a knife holder embodying the present invention it isessential that all such devices in the slitter-winding machine beinitially adjusted to bring the edge of the male knife 60 of each holderinto proper overlapping relation with respect to its cooperating fe maleknife 83. In the illustrated embodiment of the invention this isaccomplished by manually exerting downward pressure on the thimble head34 and actuating the piston-knife head assembly to the lower limitposition thereof previously described. While held in the lower limitposition, the thimble 26 is rotated either clockwise orcounter-clockwise as may be required, for example, be means of a spannerwrench engaged in one of the recesses 340 provided in the lateralperipheral surface of the thimble head 34.

Rotation of the adjustment thimble 26 as described operates to effectvertical adjustment of the piston 13 and piston rod 16 coaxially withinthe cylinder 1 and a corresponding vertical adjustment of the knife head42 and knife 60 relative to the cooperating female knife 83. Normally,it is desirable that in the lower limit position of the knife 60 thecutting edge thereof overlaps the circumference of the female knife 83 apredetermined distance, for example, about 1/6 inch, as shown in dottedlines in FIG. 6 of the drawings. This adjustment may just be madeseparately for each knife holder in the machine since the radius of theknife in each holder will vary from holder to holder due to frequentresharpening and periodic replacement of the male knifes 60 as theresult of wear.

After the male knives 60 of all of the knife holders in the machine havebeen adjusted and set as described, the machine is placed in operationand pressure fluid such as air is admitted through fitting 31 to thecylinder 1 thereby actuating the piston-knife head assembly to the lowerlimit position shown in FIG. 4 wherein the cutting edge of the blade 60is disposed in the dotted line position shown in FIG. 6. As thepiston-knife head assembly reaches its lower limit position the port 80is opened and pressure fluid in the cylinder 1 flows through theconnecting passages and ports to the chamber 45 in the knife head 42thereby actuating the flexible diaphragm to cause axial displacement ofthe mounting 51, plate 58 and male knife 60 from the inoperativeposition shown in FIG. 6 of the drawings to the operative positionthereof shown in FIG. 7, in which the cutting edge of the male knife 60is brought into cutting engagement with the web material w and thecooperating female knife 83.

Engagement of the cutting edge of the male knife 60 with the cooperatingfemale knife 83 causes a slight angular deflection of the male knife 60from the horizontal axis x to the axis y as shown in FIG. 7 causing acorresponding rocking movement of the mounting 51 relative to the knifehead 42 as shown in FIG. 7 of the drawings. This rocking movement of themounting 51 eliminates variations in the contact pressure between themale and female knives so that the contact pressure therebetween issubstantially constant at all times.

Upon completion of the slitting and winding operation of the machine thesupply of pressure fluid to the cylinder 1 is cut off thereby permittingthe spring 30 to move the piston-knife head assembly toward and to theupper limit position thereof and immediately vent pressure fluid in thediaphragm actuating chamber through the vent passage 82 in theadjustment thimble 26, thereby causing the springs 66 immediately toreturn the mounting 51, plate 58 and male knife 60 axially inwardly ofthe head 42 to the position shown in FIG. 6 of the drawings.

From the foregoing it will be apparent that the present inventionprovides a knife holder of novel construction and arrangement in whichlateral setting or shifting of the male knife is prevented and cannottake place until said male knife has attained its fully lowered positionin proper overlapping relation to the female knife of the machine. Theinvention also provides a knife holder of novel construction andarrangement wherein the contact pressure between the male and femaleknives is substantially constant at all times and in which any tendencyfor the male knife to override the female knife is eliminated. Theinvention also provides a construction in which the removal andreplacement of the male knife may be readily and easily accomplished.

While a particular embodiment of the invention has been illustrated anddescribed, it is not intended to limit the invention to such disclosureand changes and modifications may be made therein and thereto within thescope of the appended claims.

I claim:

I. A pressure fluid actuated knife holder comprising a cylinder,a=piston rod extending axially through said cylinder beyond the endsthereof and having a pressure fluid passage extending coaxially therein,a piston in the cylinder secured on said piston rod, intercooperatingmeans on the piston rod and the cylinder operable to determine retractedand projected limit positions of travel of the piston and rod axially insaid cylinder, a knife head on one end of said piston rod for movementtherewith between retracted and projected positions, knife support meansin said knife head axially shiftable therein between inner and outerpositions along an axis perpendicular to the axis of the cylinder,pressure fluid actuatable means in the knife head operable to shift saidknife support means from said inner position to an outer position, meansin said knife head defining a pressure fluid passage communicatingbetween the coaxial pressure fluid passage in said piston rod and saidpressure fluid actuatable means in the knife head, means to admitpressure fluid to the cylinder to actuate said piston from saidretracted position to said projected limit position, means in the pistonrod adjacent the other end thereof defining a pressure fluid inletpassage therein having an inner opening communicating with the coaxialpressure fluid passage in said piston rod and an outer opening forcommunication with the cylinder interior, the outer opening of saidpressure fluid inlet passage being disposed axially in the piston rod sothat said outer opening is normally closed by the cylinder in theintermediate and retracted positions of the piston rod and is open andin communication with the cylinder interior only in the projected limitposition, and means in the piston rod defining a vent passage having aninner opening communicating with said coaxial fluid passage therein andan outer opening for communication with the external atmosphere, saidvent passage being disposed axially in said piston rod and spaced withrespect to the pressure fluid inlet opening therein so that the ventouter opening is closed by the cylinder in the projected limit positionof the piston rod and is open to the atmosphere in the intermediate andretracted limit positions of said piston rod, whereby pressure fluid canflow from said cylinder to the knife head to axially shift the knifesupport from said inner position only in the projected limit position ofthe piston rod and the knife head is vented to atmosphere in saidintermediate and retracted positions of the piston rod.

2. A pressure fluid actuated knife holder as claimed in claim 1comprising means operable to return the piston and piston rod togetherwith the knife head from the projected limit position to the retractedlimit posi tion upon cut-off of pressure fluid to the cylinder.

3. A pressure fluid actuated knife holder as claimed in claim 2 whereinthe means for returning the piston and piston rod from the projectedlimit position to the retracted limit position comprises an expansioncoil spring circumscribing the piston rod.

4. A pressure fluid actuated knife holder as claimed in claim 1comprising means operable to return the knife support means to the innerposition thereof in the knife head upon venting pressure fluid from thelatter.

5. A pressure fluid actuated knife holder as claimed in claim 4 whereinthe means for returning the knife support means to the inner positioncomprises a plurality of expansion coil springs acting between the knifesupport means and an adjacent portion of the knife head.

6. A pressure fluid actuated knife holder as claimed in claim 1comprising a circular knife journaled in the knife mounting means forrotation about an axis perpendicular to the axis of the cylinder, saidknife having a circumferential cutting edge.

7. A pressure fluid actuated knife holder as claimed in claim 6 whereinthe knife mounting means is constructed and arranged for limited pivotalrocking movement in the knife head about a center located on therotation axis of the knife to permit limited angular deflection of saidknife from said axis.

8. A pressure fluid actuated knife holder as claimed in claim 6 whereinthe piston rod includes adjustable means operable to determine theprojected limit position of the piston and piston rod with respect tothe cyl inder and thereby predeterminedly set the projected limitposition of the cutting edge of the circular knife.

9. A pressure fluid actuated knife holder as claimed in claim 8 whereinthe adjustable means to determine the projected limit position of thepiston and piston rod comprises an adjustment member threaded on aportion of the piston rod at the opposite side of the piston from saidknife head and manually adjustable on said piston rod.

10. A pressure fluid actuated knife holder as claimed in claim 9 whereinthe pressure fluid inlet passage from the cylinder interior to thecoaxial pressure fluid passage in the piston rod is in the adjustmentmember.

11. A pressure fluid actuated knife holder as claimed in'claim 9 whereinthe vent passage between the coaxial fluid passage in the piston rod andthe external atmosphere is in the adjustment member.

12. A pressure fluid actuated knife holder as claimed in claim 10wherein the vent passage between the coaxial fluid passage in the pistonrod and the external atmosphere is also in the adjustment member.

13. A pressure fluid actuated knife holder as claimed in claim 7 whereinthe limited pivotal rocking movement of the knife mounting means isprovided by a peripheral surface thereon of arcuate spherical shapehaving a radius described from the center of pivotal rocking movement ofsaid knife mounting means.

14. A pressure fluid actuated knife holder as claimed in claim 9 whereinthe intercooperating means operable to determine the retracted andprojected limit positions of the piston rod axially in said cylindercomprises axially spaced means on the adjustment member disposed forcooperative engagement with the cylinder.

15. A pressure fluid actuated knife holder as claimed in claim 2comprising means operable to return the knife support means to the innerposition thereof in the knife head upon venting pressure fluid from thelatter.

16. A pressure fluid actuated knife holder as claimed in claim whereinthe knife mounting means is constructed and arranged for limited pivotalrocking movement in the knife head about a center located on therotation axis of the knife to permit limited angular deflection of saidknife from said axis.

17. A pressure fluid actuated knife holder as claimed in claim 15wherein the adjustable means to determine the projected limit positionof the piston and piston rod comprises an adjustment member threaded ona portion of the piston rod at the opposite side of the piston from saidknife head and manually adjustable on said piston rod.

18. A pressure fluid actuated knife holder as claimed in claim 15wherein the vent passage between the coaxial fluid possage in the pistonrod and the external atmosphere is also in the adjustment member.

19. A pressure fluid actuated knife holder as claimed in claim 16wherein the vent passage between the coaxial fluid passage in the pistonrod and the external atmosphere is also in the adjustment member.

20. A pressure fluid actuated knife holder as claimed in claim 19wherein the limited pivotal rocking movement of the knife mounting meansis provided by a peripheral surface thereon of arcuate spherical shapehaving a radius described from the center of pivotal rocking movement ofsaid knife mounting means.

21. A pressure fluid actuated knife holder as claimed in claim 20wherein the intercooperating means operable to determine the retractedand projected limit positions of the piston rod axially in said cylindercomprises axially spaced means on the adjustment member disposed forcooperative engagement with the cylinder.

1. A pressure fluid actuated knife holder comprising a cylinder, apiston rod extending axially through said cylinder beyond the endsthereof and having a pressure fluid passage extending coaxially therein,a piston in the cylinder secured on said piston rod, intercooperatingmeans on the piston rod and the cylinder operable to determine retractedand projected limit positions of travel of the piston and rod axially insaid cylinder, a knife head on one end of said piston rod for movementtherewith between retracted and projected positions, knife support meansin said knife head axially shiftable therein between inner and outerpositions along an axis perpendicular to the axis of the cylinder,pressure fluid actuatable means in the knife head operable to shift saidknife support means from said inner position to an outer position, meansin said knife head defining a pressure fluid passage communicatingbetween the coaxial pressure fluid passage in said piston rod and saidpressure fluid actuatable means in the knife head, means to admitpressure fluid to the cylinder to actuate said piston from saidretracted position to said projected limit position, means in the pistonrod adjacent the other end thereof defining a pressure fluid inletpassage therein having an inner opening communicating with the coaxialpressure fluid passage in said piston rod and an outer opening forcommunication with the cylinder interior, the outer opening of saidpressure fluid inlet passage being disposed axially in the piston rod sothat said outer opening is normally closed by the cylinder in theintermediate and retracted positions of the piston rod and is open andin communication with the cylinder interior only in the projected limitposition, and means in the piston rod defining a vent passage having aninner opening communicating with said coaxial fluid passage therein andan outer opening for communication with the external atmosphere, saidvent passage being disposed axially in said piston rod and spaced withrespect to the pressure fluid inlet opening therein so that the ventouter opening is closed by the cylinder in the projected limit positionof the piston rod and is open to the atmosphere in the intermediate andretracted limit positions of said piston rod, whereby pressure fluid canflow from said cylinder to the knife head to axially shift the knifesupport from said inner position only in the projected limit position ofthe piston rod and the knife head is vented to atmosphere in saidintermediate and retracted positions of the piston rod.
 2. A pressurefluid actuated knife holder as claimed in claim 1 comprising meansoperable to return the piston and piston rod together with the knifehead from the projected limit position to the retracted limit positionupon cut-off of pressure fluid to the cylinder.
 3. A pressure fluidactuated knife holder as claimed in claim 2 wherein the means forreturning the piston and piston rod from the projected limit position tothe retracted limit position comprises an expansion coil springcircumscribing the piston rod.
 4. A pressure fluid actuated knife holderas claimed in claim 1 comprising means operable to return the knifesupport means to the inner position thereof in the knife head uponventing pressure fluid from the latter.
 5. A pressure fluid actuatedknife holder as claimed in claim 4 wherein the means for returning theknife support means to the inner position comprises a plurality ofexpansion coil springs acting between the knife support means and anadjacent portion of the knife head.
 6. A pressure fluid actuated knifeholder as claimed in claim 1 comprising a circular knife journaled inthe knife mounting means for rotation about an axis perpendicular to theaxis of the cylinder, said knife having a circumferential cutting edge.7. A pressure fluid actuated knife holder as claimed in claim 6 whEreinthe knife mounting means is constructed and arranged for limited pivotalrocking movement in the knife head about a center located on therotation axis of the knife to permit limited angular deflection of saidknife from said axis.
 8. A pressure fluid actuated knife holder asclaimed in claim 6 wherein the piston rod includes adjustable meansoperable to determine the projected limit position of the piston andpiston rod with respect to the cylinder and thereby predeterminedly setthe projected limit position of the cutting edge of the circular knife.9. A pressure fluid actuated knife holder as claimed in claim 8 whereinthe adjustable means to determine the projected limit position of thepiston and piston rod comprises an adjustment member threaded on aportion of the piston rod at the opposite side of the piston from saidknife head and manually adjustable on said piston rod.
 10. A pressurefluid actuated knife holder as claimed in claim 9 wherein the pressurefluid inlet passage from the cylinder interior to the coaxial pressurefluid passage in the piston rod is in the adjustment member.
 11. Apressure fluid actuated knife holder as claimed in claim 9 wherein thevent passage between the coaxial fluid passage in the piston rod and theexternal atmosphere is in the adjustment member.
 12. A pressure fluidactuated knife holder as claimed in claim 10 wherein the vent passagebetween the coaxial fluid passage in the piston rod and the externalatmosphere is also in the adjustment member.
 13. A pressure fluidactuated knife holder as claimed in claim 7 wherein the limited pivotalrocking movement of the knife mounting means is provided by a peripheralsurface thereon of arcuate spherical shape having a radius describedfrom the center of pivotal rocking movement of said knife mountingmeans.
 14. A pressure fluid actuated knife holder as claimed in claim 9wherein the intercooperating means operable to determine the retractedand projected limit positions of the piston rod axially in said cylindercomprises axially spaced means on the adjustment member disposed forcooperative engagement with the cylinder.
 15. A pressure fluid actuatedknife holder as claimed in claim 2 comprising means operable to returnthe knife support means to the inner position thereof in the knife headupon venting pressure fluid from the latter.
 16. A pressure fluidactuated knife holder as claimed in claim 15 wherein the knife mountingmeans is constructed and arranged for limited pivotal rocking movementin the knife head about a center located on the rotation axis of theknife to permit limited angular deflection of said knife from said axis.17. A pressure fluid actuated knife holder as claimed in claim 15wherein the adjustable means to determine the projected limit positionof the piston and piston rod comprises an adjustment member threaded ona portion of the piston rod at the opposite side of the piston from saidknife head and manually adjustable on said piston rod.
 18. A pressurefluid actuated knife holder as claimed in claim 15 wherein the ventpassage between the coaxial fluid possage in the piston rod and theexternal atmosphere is also in the adjustment member.
 19. A pressurefluid actuated knife holder as claimed in claim 16 wherein the ventpassage between the coaxial fluid passage in the piston rod and theexternal atmosphere is also in the adjustment member.
 20. A pressurefluid actuated knife holder as claimed in claim 19 wherein the limitedpivotal rocking movement of the knife mounting means is provided by aperipheral surface thereon of arcuate spherical shape having a radiusdescribed from the center of pivotal rocking movement of said knifemounting means.
 21. A pressure fluid actuated knife holder as claimed inclaim 20 wherein the intercooperating means operable to determine theretracted and projected limit positions of the piston rod axially insaid cylinder comprises axially spaced means on the adjustment memberdisposed For cooperative engagement with the cylinder.